Crack arrester

ABSTRACT

A crack arrester and a pipeline containing at least one of the same wherein the crack arrester is a cylindrical part for use inline in a pipeline, the cylindrical part having a longitudinal impact strength substantially greater than its transverse impact strength.

United States Patent Loncaric 1 CRACK ARRESTER [72] Inventor: Rado G.Loncaric, Dallas, Tex.

[73] Assignee: Atlantic Richiield Company, New

.York,N.Y.

22 Filed: Jan.18, 1971 21 Appl.No.: 107,296

[52] US. Cl. ...285/286, 29/417, 29/477, 285/422, 138/155, 138/178 [51]Int. Cl ..Fl6l 13/02 [58] Field of Search ..138/177,170,171,155,178;29/417, 477, DIG. 17; 285/286, 422

[56] References Cited UNITED STATES PATENTS 3,096,105 7/1963 Risley..285/286 351,987 11/1886 Lewis ..138/177 1 Oct. 17,1972

2,346,392 4/1944 Protin ..138/177 1,908,889 5/1933 Browne ..138/177 X3,131,727 5/1964 Powellm, ..138/177 X 2,067,801 1/1937 Taylor ..138/171X 2,883,246 4/1959 Hatch ..138/155 X 1,483,450 2/1924 Kenney ..29/4771,483,451 2/1924 Kenney ..29/477 Primary Examiner-Herbert F. RossAttorney--B1ucher S. Tharp and Roderick W. Mac- Donald 5 7] ABSTRACT Acrack arrester and a pipeline containing at least one of the samewherein the crack arrester is a cylindrical part for use in-line in apipeline, the cylindrical part having a longitudinal impact strengthsubstantially greater than its transverse impact strength.

7 Claims, 7 Drawing Figures PATENTEUum 11 m2 3.698.746

PRIOR ART FIG.2

INVENTOR:

RADO G. LONCAR/C FIG. 7 WM$ M 4f ATTORNEYS CRACK ARRESTER BACKGROUND OFTHE INVENTION l-leretofore in the forming of right cylindrical pipesections, which sections are later joined in an end-toend fashion inopen communication with one another to provide a pipeline, each pipesection has been formed from a metal plate which is substantially longerthan it is thick or wide. The longitudinal orlong axis of the plate isformed by rolling or otherwise elongating a shorter block of metal untilthe desired length parallel to the longitudinal axis is reached. Theelongated plate is then folded about is longitudinal axis to form thecylindrical pipe section and the abutting sides of the folded plate arejoined to one another such as by welding. Thus, the longitudinal axis ofthe plate is also the longitudinal axis of the pipe section and issubstantially parallel to the final longitudinal axis of the pipeline.

In a pipeline which is in use, a fracture or crack at one spot in thepipeline can be caused by various sources, for example by corrosion,impact from an external force such as a trenching machine accidentallystriking the pipeline, earthquakes, and the like. When a crack doesoccur in a pipeline, if the rate of release of pressure in the fluid(liquid and/or gas) carried in the pipeline is slower than the speed atwhich the crack in the pipeline occurs, the crack may becomeselfpropagating since it will always be occurring at the tip of a crackwhich is a point under stress of pressure. When a crack occurs in apipeline under pressure, the speed at which the pressure is releaseddepends upon the rate at which the decompression wave can travel andthis rate depends in large part on the characteristics of the fluidcarried in the pipeline. The rates of decompression are comparativelyslow in gas pipelines as opposed to liquid pipelines. For example, therates of decompression in gas pipelines are about 1,400 feet per secondwhereas a crack, once started in the pipeline, can travel at speeds ashigh as 2,500 feet per second. This is an example of what is calledbrittle crack propagation. There is also what is known as shear crackpropagation in which case the rate of decompression and the rate ofcrack propagation are both substantially lower than for brittle crackpropagation. Thus, in a gas pipeline the decompression wave can travelsubstantially behind the point at which fracturing is occurring so thatthe decompression wave has difficulty catching up with the incipientfracturing. The crack will then become self-propagating and as such cantravel along the length of the pipeline for miles. The sameconsiderations are not true in pipelines carrying liquids such as crudeoil because the decompression wave in a pipeline carrying crude oil cantravel at speeds up to 4,500 feet per second which is substantiallyfaster than the 2,500 feet per second of the fracture. Thus, thedecompression wave in a crude oil pipeline will overtake the fracture inshort order at which time the interior of the pipeline is decompressedand the crack stopped. Accordingly, a self-propagating fracture whichcan travel for miles along the length of a pipeline before stopping isnot the risk in a crude oil pipeline that it is in a compressed gaspipeline such as a natural gas pipeline.

In a gas pipeline it is quite important to have some means present forstopping a self-propagating fracture.

2 SUMMARY OF THE INVENTION According to this invention there is provideda pipeline crack (fracture) arrester which comprises at least onecylindrical part, each cylindrical part being of a size andconfiguration adapted for in-line use in a pipe line and having alongitudinal impact strength substantially greater than its transverseimpact strength. This invention is operable in stopping both brittlecrack propagation and shear crack propagation.

In the situation described hereinabove wherein a pipeline is composed ofa plurality of sections of pipe wherein the longitudinal axis of eachsection of pipe is parallel to the longitudinal axis of the elongatedplate from which the section was made, each section of pipe is uniformlyweak in a transverse direction so that a self-propagating fracture willmeet no increase in resistance and therefore will not be slowed down asit travels from pipe section to pipe section along the length of thepipeline.

in the situation described hereinabove wherein a metal block iselongated more in one direction than in another to provide a plate whichis formed parallel to its longitudinal direction into a pipe section,the transverse impact strength of that pipe section and all other pipesections similarly formed, will be substantially greater than thelongitudinal impact strength of that pipe section. The terms transverseimpact strength and longitudinal impact strength" will be defined inmore detail hereinafter, but suffice it to say that in the normalpipeline in use today each pipe section comprising that pipeline has asubstantially stronger transverse impact strength than longitudinalimpact strength and it has been found that this condition aids ratherthan hinders a self-propagating fracture.

Accordingly, by the use of a crack arrester according to this inventiona self-propagating fracture can be slowed to the point that thedecompression wave catches up with it thereby allowing decompression ofthe pipeline at the point where fracturing is being initiated andstopping the propagation of the crack altogether.

This invention also relates to a pipeline formed from a plurality ofsections of pipe, each section of pipe having a longitudinal impactstrength substantially weaker than its transverse impact strength,wherein at least one of the crack arresters according to this inventionare fixed in open communication in the pipeline at at least oneintermediate point between the ends of the pipeline.

The crack arrester of this invention is useful in all types of pipelinesincluding those carrying liquids, particularly where the liquidstransmit a decompression wave at rates below the rate of travel of afracture in the pipeline This invention is particularly useful in allpipelines which carry a compressed gas, particularly natural gas, sincethis type of fluid can transmit the decompression wave at ratessubstantially below the rate of travel of the crack and are thereforemuch more susceptible to self-propagating fracturing.

Accordingly, it is an object of this invention to provide a new andimproved crack arrester for pipelines. It is another object of thisinvention to provide a new and improved pipeline which will stop aself-propagating fracture once initiated. It is another object toprovide a new and improved apparatus which will stop the propagation ofa crack in a pipeline, particularly in a pipeline carrying a gas underpressure. It is another object to provide a new and improved pipeline,particularly a natural gas pipeline, capable of extinguishing fractureswhich wouldotherwise be self-propagating along a substantial portion ofthe length of that pipeline.

Other aspects, objects, and advantages of this invention will beapparent to those skilled in the art from this disclosure and theappended claims.

DETAILED DESCRIPTION OF THE INVENTION FIGS. 1 through 3 show aconventional prior art process for forming a pipe section.

FIGS. 4 and 5 show the formation of a crack arrester according to thisinvention.

FIG. 6 shows a pipeline employing a variety of crack arresters withinthis invention.

FIG. 7 shows another form of crack arrester within the scope of thisinvention. N

More specifically, FIG. I shows a block 1 of metal. The block can becomposed of any malleable metal or alloy of two or more metals (with orwithout nonmetallic additives such ascarbon and boron) which can be hotrolled and/or cold rolled into an elongated plate. Generally, any metaluseful in making metal pipe can be employed in making the crackarresters of this invention so that the crack arrester of this inventioncan be formed of the materials as described for block 1.

Block 1 is passed one or more times between one or more pairs of spacedapart rollers, e.g., rollers 2 and 3. The space between rollers 2 and 3is less than the height 4 of block 1 so that the block is elongatedsubstantially' in its direction of rolling 5 as shown by portion 6ofblock l which is issuing from between rolls 2 and 3.

The rolling procedure can be carried out while the block is either hotor cold and can be repeated a number of times until block 1 has takenthe elongated I plate configuration shown by plate 10. In plate 10' thelongitudinal axis 11 is parallel to the rolling direction 5 and issubstantially. longer than the width 12 or thickness 13. It should beunderstood that there can be some amount of rolling of plate 10' normalto or at other angles to longitudinal axis 1 l to achieve a desiredwidth 12, while retaining a primary rolling direction 5 which isparallel to the longitudinal axis 11 of the resulting plate 10'.

As shown in FIG. 2, plate 10' is formed into a U configuration byfolding about (parallel to) longitudinal axis 11 until sides 15 and 16which are parallel to axis 11 and rolling direction 5, are pointedupwardly.

As shown in FIG. 3 Ud plate 10' of FIG. 2 is formed into a cylindricalconfiguration 10 by bringing sides 15 and 16 into abutment and joiningthe sides along the.

length thereof such as by welding to form a substantially straight seam17. When sides 15 and 16 are joined in this manner a substantiallystraight seamed pipe section is formed. 7

It should be noted that the resulting pipe section 10 was formed fromroller plate 10' by bending the plate about its longitudinal axis 11 sothat the longitudinal axis 11 of pipe section 10 is the same and isparallel to the primary rolling direction 5. Thus, when the pipe sectionof FIG. 3 is joined in an end-to-end pipeline fashion all sections inthe pipeline will have their longitudinal axes 11 parallel to thelongitudinal axis of the pipeline and also parallel to the primaryrolling direction of the plate from which each pipe section was formed.

A procedure for determining strength characteristics of a particularmetal is known as the Charpy V-Notch Impact Test which is fully andcompletely disclosed as ASTM Test E 23-66. In this test a specimen iscut from the metal to be tested, a notch according to certainspecifications cut' in the specimen, and the specimen tested accordingto precise procedures to determine how'many foot pounds of energy'isabsorbed by the specimen upon being impacted with a standard force.

In making tests on the prior art pipe section shown in FIG. 3, specimenswould be taken from the pipe section parallel to the longitudinal axis11 as shown by specimen 18 and transverse to longitudinal axis 11 asshown by specimen 19. Longitudinal specimen 18 would be notched in adirection normal to the direction of longitudinal axis 11 as shown bynotch-20 so that the specimen when tested would break in a transversedirection as shown by arrow 21. Thus a longitudinal test specimenmeasures transverse impact strength. Transverse specimen l9"would benotched parallel to longitudinal axis 11 as shown by notch 22 andtherefore would fracture parallel to longitudinal axis 11 as shown byarrow 23. Therefore a transverse test specimen measures longitudinalimpact strength.

For reasons not completely understood, in a pipe section such as thatshown in FIG. 3 which has been formed so that its longitudinal axis 11is parallel to the primary rolling direction 5, the transverse impactstrength as measured by longitudinal specimen 18 is substantiallygreater than the longitudinal impact strength as measured by transversespecimen 19. Thus, a crack propagating along the length of pipe section10 substantially parallel to the longitudinal axis 11 would be workingagainst the weaker longitudinal impact strength as measured bytransverse specimen l9 and would encounter no great or increasingresistance as it moved along the length of pipe section 10 and othersimilar pipe sections down the length of the pipeline. Thus, pipesection 10 and all similar pipe sections are very susceptible to aself-propagating longitudinal fracture situation.

A crack arrester according to this invention can be formed from aportion of plate 10' of FIG. 1 by taking a portion 30 of plate 10' andforming it into a U configuration transverse to both its longitudinalaxis 11 and primary direction of rolling 5. For example, section 30 ofplate 10 in FIG. 1 is taken by cutting along dotted line 31 (line 31identifies the left end of portion-30, the opposing right end being end32). Section 30 is then formed into a U configuration as shown in FIG. 4so that ends 31 and 32 extend upwardly. This is completely contrary tothe prior art step shown in FIG. 2 wherein plate 10' is bent from sideto side, side 15 to side 16, since portion 30 is bent from end to end,end 31'to end 32.

FIG. 5 shows Ud portion 30 formed into a cylindrical configuration bybringing ends 31 and 32 into abutment and fixing them together such asbe welding with a substantially Straight seam 33.

Portion 30 has been formed into a cylindrical configuration transverseto both the longitudinal axis 11 of plate and its primary direction ofrolling 5. In this situation the transverse impact strength of portion30 measured by longitudinal specimen 36 will be substantially less thanthe longitudinal impact strength measured by transverse specimen 35.

FIG. 6 shows a pipeline 40 formed from a plurality of conventionallyprepared pipe sections 10. Normally, pipe sections 10 would be placed inan end-to-end pipeline fashion in open communication with one anotherand welded or otherwise coupled together as such. However, according tothis invention at least two of the pipe sections 10 in the pipeline areseparated from one another by a crack arrester 41.

The crack arrester is of a size substantially the same both in internaland external diameter so that it is adapted for use in-line in thepipeline just as pipe sections 10 are adapted for in-line use in thepipeline.

Arrester 41 can be composed of one or more cylindrical parts. As shownin FIG. 6 arrester 41 is composed of two cylindrical parts 42 and 43joined in an end-to-end pipeline fashion such as by welding and thelike. Thus, a single arrester 41 can be composed of one cylindrical.part or two or more cylindrical parts joined together in pipelinefashion. In FIG. 6 cylindrical part 42 can be one portion 30 of FIG. 5while part 43 is yet another portion 30 of FIG. 5.

Each cylindrical part in an arrester according to this invention has alongitudinal axis parallel to the longitudinal axis 11 of pipe sections10 but the length of each part parallel to its longitudinal axis may besubstantially shorter than the length of each pipe section 10. Thelength of a cylindrical part in an arrester parallel to its longitudinalaxis may even be less than its inside diameter, but this length is stillconsidered to be parallel to its longitudinal axis since it is parallelto the longitudinal axis 11 of pipe sections 10 and to the longitudinalaxis of the pipeline. Of course, each arrester can be of any desiredlength, even longer than a pipe section 10, if desired. It is preferredthat when two or more cylindrical sections 42 and43 are employed to forma single arrester, the straight seam welds such as seam 33 in FIG. 5 notbe aligned with one another. It is preferred that the seams in adjacentcylindrical parts of an arrester are rotationally spaced from oneanother.

More than one arrester 41 can be employed along the length of thepipeline as desired and as depends upon the particular materialsemployed for the pipe sections, the arresters, the fluid carried by thepipeline, and the likelihood of a crack occurring. Therefore, the numberof individual arresters employed along a given pipeline can be onesomewhere intermediate the ends of the pipeline, one between each pairof pipe sections as shown in FIG. 6, or any number in-between.

The crack arrester of this invention need not have a transverse impactstrength substantially less than the longitudinal impact strength. Itcan be sufficient if the crack arrester has an impact strength which isat angle between transverse and longitudinal and which is substantiallyless than its longitudinal impact strength. This is achieved byemploying a cylindrical part 44 which is spirally wrapped about itslongitudinal axis and primary rolling direction thereby providing acylindrical part which is spirally seamed (45) rather than straightseamed (parts 42 and 43 and portions 30 of FIG. 5).

Straight seamed and spirally seamed cylindrical parts can be employedalternatively, joined, in sequence, or in any other desired combinationalong the length of the pipeline. For example, besides the possibilityshown in FIG. 6, a spirally seamed crack arrester could be emplacedbetween cylindrical parts 42 and 43 or on either or both sides of thoseparts, and the like.

When a fracture is initiated for some reason, for example, in the leftmost pipe section 10 of FIG. 6 at point 47, the crack will propagateparallel to the longitudinal axis 11 since pipe section 10 has astronger transverse impact strength than longitudinal impact strengthand the crack will travel toward both ends of pipe section 10 asrepresented by arrows 56 and 57. The end of the crack traveling parallelto arrow 57 will run into arrester 41 which has a stronger longitudinalimpact strength because the transverse impact strength of cylindricalpart 42 is the same as the longitudinal impact strength of pipe section10, cylindrical part 42 being formed as portion 30 of FIG. 5. Thefracture propagation will slow when it encounters tougher cylindricalpart 42 and by the time it has traveled to some point between end 48 andend 49 of arrester 41 it will have been slowed in its propagationsufficiently for the decompression wave to catch up with it anddecompress the pipeline in the area where the fracture is propagatingthus stopping the propagation of the crack. The crack propagating in thedirection of arrow 56 will travel in that direction until stopped inlike manner by another crack arrester, but if there is not another crackarrester in the direction of arrow 56 the crack could propagate formiles along the length of the pipeline before being stopped by chance.

Arrester 44 of FIG. 6 is shown more indetail in FIG. 7. Arrester 44 isformed from a flat plate such as plate 10' of FIG. 1 but instead ofbeing folded parallel to longitudinal axis 11 in a side 15 to side 16fashion to provide a straight seam 17 which is substantially parallel tolongitudinal axis 11, plate 10 is folded spirally about longitudinalaxis 11 so that edges 15 and 16 meet one another in a spiral to providea spiral seam 45. In this manner longitudinal axis 11 of plate 10' inFIG. 1 and the primary rolling direction 5 follow the spiral of seam 45.Thus, the greater impact strength (which is the transverse strength inthe pipe section of FIG. 3 and the longitudinal strength in portion 30of FIG. 5) is at an angle between transverse direction 50 andlongitudinal direction 51. The angle 52 in which the greater impactstrength will occur will vary widely between transverse direction 50 andlongitudinal direction 51 but will generally be at least about 10 fromtransverse as represented by angle 53 and at least about 10 fromlongitudinal as represented by angle 54.

The arresters of this invention can be formed from any material which isnow being formed into metal pipe. Such materials include steel, copper,stainless steel, and the like. A particularly useful material is steelwhich contains primarily (at least about 50 weight percent based on thetotal weight of the steel) ferrite with minor amounts (less than 50weight percent based on the total weight of the steel) of austenite,martensite, and the like.

Although this invention has been disclosed in relation to the use ofseamed pipe sections, the invention is equally applicable to seamlesspipe sections or any other type of pipe section so long as thelongitudinal impact strength of the pipe section is substantially lessthan its transverse impact strength, in which case the arrestersaccording to this invention which have a longitudinal impact strengthsubstantially greater than their transverse impact strength can be usedto good avail in stopping a self-propagating fracture. In like mannerthe arresters of this invention, besides being seamed, can be seamlessso long as they meet the above requirements concerning relative impactstrengths.

EXAMPLE A carbon steel consisting essentially of ferrite with a minoramount of retained austenite therein and having a tensile strength ofabout 75,000 psi is initially in a 1 foot square block and is hot rolledas shown in FIG. 1 with both transverse and longitudinal rolling to formplate 10' which has a thickness 13 of about one-half inch, a width 12 ofabout feet, and a length parallel to the primary direction of rolling 5and parallel to longitudinal axis 1 1 of about 60 feet.

The plate when formed into a pipe section as shown in F K]. 3 has atransverse impact strength as measured by longitudinal specimen 18 of120 to 150 foot-pounds and a longitudinal impact strength as measured bytransverse specimen 19 of 50 to 80 foot-pounds.

Portion 30 taken from plate of FIG. 1 and formed into a cylindrical partas shown in FIG. 5, portion 30 being 5 feet in width 32 and 6 feet long,forms a cylindrical part 30 of a size adapted to be welded to either endof pipe section 10 of FIG. 3 in open communication therewith to form aportion of the pipeline. However, cylindrical part 30 has a transverseimpact strength measured by longitudinal specimen 35 of 50 to 80foot-pounds and a longitudinal impact strength as measured by transversespecimen 36 of l20 to 150 foot-pounds.

Thus, a fracture propagating in pipe section 10 parallel to itslongitudinal axis 11 is working against a longitudinal impact strengthof 50 to 80 foot-pounds but when the crack reaches cylindrical part 42of crack arrester 41 which is composed of portion 30 of FIG. 5, thecrack immediately encounters a longitudinal impact strength of 120 to150 foot-pounds which slows the rate of crack propagation to the pointwhere the following decompression wave catches up to the tip of thecrack at which point fracturing in unfractured metal is just beginningand decompresses the interior of the pipeline at this point therebyarresting the crack propagation.

Reasonable variations and modifications are possible within the scope ofthis disclosure without departing from the spirit and scope of thisinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a pipeline formed from a plurality of sections of pipe eachsection having a longitudinal impact strength substantially less I thanits transverse impact strength, the improvement comprising at least onecrack arrester fixed in open communication in said pipeline at at leastone intermediate point between the ends of said pipeline, each crackarrester comprising at least one cylindrical part, each cylindrical parthaving an impact strength at an angle between transverse andlongitudinai which is substantially greater than the longitudinai impactstrength of each section of pipe, said angle between transverse andlongitudinal is in the range of from about 10 from transverse to about10 from longitudinal.

\ 2. A pipeline according to claim 1 wherein a plurality of said crackarresters are fixed in-line in said pipeline at spaced apart pointsaiong the length thereof.

3. A pipeline according to claim 1 wherein each crack arrester comprisesa spirally seamed cylindrical part whose impact strength at an anglebetween transverse and longitudinal is substantially greater than itstransverse impact strength.

4. A pipeline according to claim 1 wherein said impact strength at anangle between transverse and longitudinal is at least about 25 percentgreater than said transverse impact strength.

5. A pipeline according to claim 1 wherein each cylindrical part isformed from at least one rolled plate which has been formed into acylindrical configuration,

and the primary direction of rolling of said plate is at an anglebetween transverse and longitudinal in the cylindrical configuration.

6. A pipeline according to claim 1 wherein said plate is steel plate.

7. A pipeline according to claim 6 wherein said steel is primarilyferritic with minor amounts of austenite and/or martensite.

P0-1050 UNITED STATES PATENT OFFICE 9 CERTIFICATE OF CORRECTION PatentNO. 3,698,7u6 Dated October 17, 1972 Inventor(s) Rado G. LOnCa JI'iC EIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Cclurm 8, line H2, "claim 1" should read ---claim 5--- Signed and sealedthis 13th day of March 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. In a pipeline formed from a plurality of sections of pipe eachsection having a longitudinal impact strength substantially less thanits transverse impact strength, the improvement comprising at least onecrack arrester fixed in open communication in said pipeline at at leastone intermediate point between the ends of said pipeline, each crackarrester comprising at least one cylindrical part, each cylindrical parthaving an impact strength at an angle between transverse andlongitudinal which is substantially greater than the longitudinal impactstrength of each section of pipe, said angle between transverse andlongitudinal is in the range of from about 10* from transverse to about10* from longitudinal.
 2. A pipeline according to claim 1 wherein aplurality of said crack arresters are fixed in-line in said pipeline atspaced apart points along the length thereof.
 3. A pipeline according toclaim 1 wherein each crack arrester comprises a spirally seamedcylindrical part whose impact strength at an angle between transverseand longitudinal is substantially greater than its transverse impactstrength.
 4. A pipeline according to claim 1 wherein said impactstrength at an angle between transverse and longitudinal is at leastabout 25 percent greater than said transverse impact strength.
 5. Apipeline according to claim 1 wherein each cylindrical part is formedfrom at least one rolled plate which has been formed into a cylindricalconfiguration, and the primary direction of rolling of said plate is atan angle between transverse and longitudinal in the cylindricalconfiguration.
 6. A pipeline according to claim 1 wherein said plate issteel plate.
 7. A pipeline according to claim 6 wherein said steel isprimarily ferritic with minor amounts of austenite and/or martensite.